Commonly used living body authentication apparatuses using fingerprints, which are a kind of living body feature, to authenticate individuals employ a method using a critical angle of total reflection by a triangular prism (for example, see Patent Literature 1). The method involves reading bumpiness (ridges and furrows) of a skin surface, which enables a fingerprint image to be easily obtained with high contrast. The method has thus highly compatible with “fingerprinting” wherein fingerprints are collected by impressing an inked fingertip against paper, and the method has been used in judicial and police purposes.